The Growth-Promoting Mechanism of Brevibacillus laterosporus AMCC100017 on Apple Rootstock Malus robusta

Plant growth-promoting rhizobacteria(PGPR) located in rhizobacteria soil are beneficial to plant growth and development. A PGPR strain AMCC100017 of Brevibacillus laterosporus synthesizes the plant hormone IAA in a tryptophan-dependent manner. In this study, the AMCC100017 strain was used to treat Malus robusta, an excellent natural rootstock for apple production, and assess its ability to promote growth. The fresh weight, dry weight, plant height, and lateral root growth of M. robusta were significantly increased with treatment. The presence of the AMCC100017 strain increased IAA content in M. robusta and promoted root secretion of tryptophan. Colonization of the strain in the roots allowed continuous synthesis of IAA and promoted plant growth. In addition, the photosynthetic efficiency in leaves increased after microbial treatment, and the utilization of nitrogen, zinc, iron, copper and magnesium in leaves was increased, which was conducive to photosynthesis.Interestingly, the activities of CAT and SOD, as well as the contents of ROS in plants colonized by AMCC100017 were increased compared to control plants, but the activities of POD and MDA contents were decreased. AMCC100017 strain affected the antioxidant capacity and stress resistance of plants. AMCC100017 strain increased the content of soluble protein and soluble sugar in plants, improved plant metabolic activity and stress resistance. Therefore, AMCC100017 not only increased IAA content and photosynthetic efficiency to promote M. robusta growth, but also affected plant through multiple metabolic pathways.

Predictive Decision and Reliable Accessing for UAV Communication in Space-Air-Ground Integrated Networks

The cooperation of multiple Unmanned Aerial Vehicles(UAVs) has become a promising scenario in Space-Air-Ground Integrated Networks(SAGINs) recently due to their widespread applications,where wireless communication is a basic necessity and is normally categorized into control and nonpayload communication(CNPC) as well as payload communication. In this paper, we attempt to tackle two challenges of UAV communication respectively on establishing reliable CNPC links against the high mobility of UAVs as well as changeable communication conditions, and on offering dynamic resource optimization for Quality-of-Service(QoS) guaranteed payload communication with variable link connectivity. Firstly, we propose the concept of air controlling center(ACC), a virtual application equipped on the infrastructure in SAGINs, which can collect global information for estimating UAV trajectory and communication channels. We then introduce the knapsack problem for modelling resource optimization of UAV communication in order to provide optimal access points for both CNPC and payload communication. Meanwhile, using the air controlling information, predictive decision algorithm and handover strategy are introduced for the reliable connection with multiple access points. Simulation results demonstrate that our proposal ensures an approximate always-on reliable accessing of communication links and outperforms the existing methods against high mobility,sparse distribution, and physical obstacles.

Energy Efficiency Optimization for D2D Communications Based on SCA and GP Method

In this paper, we propose an energy-efficient power control scheme for device-to-device(D2D) communications underlaying cellular networks, where multiple D2D pairs reuse the same resource blocks allocated to one cellular user. Taking the maximum allowed transmit power and the minimum data rate requirement into consideration, we formulate the energy efficiency maximization problem as a non-concave fractional programming(FP) problem and then develop a two-loop iterative algorithm to solve it. In the outer loop, we adopt Dinkelbach method to equivalently transform the FP problem into a series of parametric subtractive-form problems, and in the inner loop we solve the parametric subtractive problems based on successive convex approximation and geometric programming method to obtain the solutions satisfying the KarushKuhn-Tucker conditions. Simulation results demonstrate the validity and efficiency of the proposed scheme, and illustrate the impact of different parameters on system performance.

Impact of Phase Noise on TDMS Based Calibration for Spaceborne Multi-Beam Antennas

For spaceborne multi-beam antennas(MBAs), time division multiplexed switching(TDMS) based calibration receiver can reduce implementation costs effectively and is very suitable for large-scale applications. However, in practice, random phase noise imposed by noisy local oscillators can cause significant performance degradation in TDMS-based calibration systems. Characterization of phase noise effects is therefore crucial for practical applications. In this paper, we analyze the impact of phase noise on the calibration performance for a MBA system. Specifically, we derive the relationship between the probability of correct amplitude/phase estimation and various practical factors involving the signal-to-noise ratio(SNR), the standard deviation of phase noise, the given tolerance region, and the length of the spreading code. The results provide high efficiency for evaluating the calibration performance of the MBAs based on TDMS, especially for precisely anticipating the impact of phase noise. Finally, the accuracy of the derived results is assessed by simulations in different scenarios.

Robust two-stage reduced-dimension STAP algorithm andits performance analysis

A new two-stage reduced-dimension space-time adaptiveprocessing （STAP） approach, which combines the subcoherentprocessing interval （sub-CPI） STAP and the principalcomponent analysis （PCA）, is proposed to achieve a more enhancedconvergence measure of effectiveness （MOE）. Furthermore,in the case of the subspace leakage phenomenon, theproposed STAP method is modified to hold the fast convergenceMOE by using the covariance matrix taper （CMT） technique. Bothsimulation and real airborne radar data processing are providedto analyze the convergence MOE performance of the proposedSTAP methods. The results show the proposed method is moresuitable for the practical radar applications when compared withthe conventional sub-CPI STAP method.

Robust or nonrobust: On MC-DS-CDMA acquisition in LEO satellite communications

Low Earth Orbit(LEO)satellite communications can provide global coverage in the sixth generation communication(6G)networks.To combat the strong Partial Band Interferences(PBIs)and multipath fading in LEO satellite communication systems,the Multicarrier Direct Sequence Code Division Multiple Access(MC-DS-CDMA)technique is a promising alternative to the traditional Single-carrier Direct Sequence Code Division Multiple Access(SC-DS-CDMA)system for its advantages of high bandwidth efficiency,superior interference rejection capability,and low complexity of parallel signal processing.However,limited studies have been conducted on the performance analysis of MC-DS-CDMA acquisition systems in the presence of a large Doppler shift,a unique characteristic of LEO satellite communications.To bridge this gap,we investigate the performance of MC-DS-CDMA systems with two-dimensional acquisition and noncoherent equal gain combining over Rician fading channel in the presence of the Doppler shift and PBIs.The performance metrics are detection probability and Mean Square Error(MSE)of the Doppler factor and delay.Specifically,we derive the closed-form expressions for the MSE and the Probability Density Function(PDF)of the acquisition decision variable and obtain the detection probability.We conduct extensive numerical experiments to verify the theoretical analysis and performance gain of MC-DSCDMA over the SC-DS-CDMA.The results show that MC-DS-CDMA with two-dimensional acquisition is more robust to multipath Rician fading than SC-DS-CDMA.Moreover,MC-DS-CDMA outperforms SC-DS-CDMA regarding the detection probability and MSE when combating the strong PBIs.

Passive Beamforming Design for Intelligent Reflecting Surface Assisted MIMO Systems

Intelligent reflecting surfaces(IRSs)constitute passive devices,which are capable of adjusting the phase shifts of their reflected signals,and hence they are suitable for passive beamforming.In this paper,we conceive their design with the active beamforming action of multiple-input multipleoutput(MIMO)systems used at the access points(APs)for improving the beamforming gain,where both the APs and users are equipped with multiple antennas.Firstly,we decouple the optimization problem and design the active beamforming for a given IRS configuration.Then we transform the optimization problem of the IRS-based passive beamforming design into a tractable non-convex quadratically constrained quadratic program(QCQP).For solving the transformed problem,we give an approximate solution based on the technique of widely used semidefinite relaxation(SDR).We also propose a low-complexity iterative solution.We further prove that it can converge to a locally optimal value.Finally,considering the practical scenario of discrete phase shifts at the IRS,we give the quantization design for IRS elements on basis of the two solutions.Our simulation results demonstrate the superiority of the proposed solutions over the relevant benchmarks.

A Quadratic Constraint Total Least-squares Algorithm for Hyperbolic Location

A novel algorithm for source location by utilizing the time difference of arrival (TDOA) measurements of a signal received at spatially separated sensors is proposed. The algorithm is based on quadratic constraint total least-squares (QC-TLS) method and gives an explicit solution. The total least-squares method is a generalized data fitting method that is appropriate for cases when the system model contains error or is not known exactly, and quadratic constraint, which could be realized via Lagrange multipliers technique, could constrain the solution to the location equations to improve location accuracy. Comparisons of performance with ordinary least-squares are made, and Monte Carlo simulations are performed. Simulation results indicate that the proposed algorithm has high location accuracy and achieves accuracy close to the Cramer-Rao lower bound (CRLB) near the small TDOA measurement error region.

Hybrid Precoding for Cluster-Based Multi-Carrier Beam Division Multiple Access in Terahertz Wireless Communications

Terahertz(THz)wireless communication has the capability to connect massive devices using its ultra-large spectrum resource.We propose a hybrid precoding scheme for the cluster-based multi-carrier beam division multiple access(MC-BDMA)to enable THz massive connections.Both the inter-beam interference and inter-band power leakage in this system are considered.A mathematical model is established to analyze and reduce their effects on the THz signal transmission.By considering the peculiarities of THz channels and characteristics of THz hardware components,we further propose a three-step hybrid precoding algorithm with low complexity,where the received signal power enhancement,the inter-beam interference elimination,and the inter-band power leakage suppression are conducted in succession.Simulation results are presented to demonstrate the high spectrum efficiency and high energy efficiency of our proposed algorithm,especially in the massive-connection scenarios.

基于扩维域能量弥散的隐蔽通信

无线通信技术是现今蓬勃发展的数据时代不可或缺的重要信息传输手段之一,而无线数据的安全性更是构建数据时代的磐石.在某些特殊应用场景中,发送方不但要保障信息内容的安全,甚至要做到无线信号传输的行为不被侦收发现.面对严峻的无线电侦收威胁,传统的隐蔽通信手段是基于某一个或两个维域进行能量弥散以降低被侦测概率,如基于扩频的码分多址接入技术将能量弥散到频域,短时猝发技术将能量弥散在时域的多个离散时段,短时猝发与跳频结合的技术将能量弥散在时、频两域.本文首先回归无线传输过程中信号能量弥散的物理本质,将隐蔽通信模型从能量在单维域弥散扩展至时–频–空的多维域能量弥散.即利用此模型并借助无线电传播理论以及数字信号处理方法等工具对无线信号能量在时–频–空3个维域的能量弥散进行建模,设计了侦听方面向时–频–空维域的能量检测器.接下来,在此多维域能量检测模型下,推导了侦听方收集能量的表达式,侦听方使用平均噪声能量作为门限的检测概率上下边界表达式,以及在纽曼–皮尔逊(Neyman-Pearson)能量检测器下的检测概率上下边界表达式.然后,结合理论推导分析、归纳并证明了扩维域能量弥散以实现隐蔽通信思路的正确性.然后,结合仿真结果,从博弈的角度讨论了在多维域能量检测模型下发送方隐蔽性存在的条件以及侦听方接收机的改进策略.最后,针对实际工程,揭示了无线隐蔽通信系统隐蔽性与可靠性这一内生矛盾及相互作用机理,进而给出了实现无线隐蔽传输的原理及技术途径.

面向空间信息网络的隐蔽通信技术综述

空间信息网络是由部署在不同轨道、执行不同任务的航天器、航空器,以及地面通信设施构成的空天地一体化网络,具有超大规模、多层拓扑结构、开放的通信环境、支持多种业务等特点,通过卫星节点、空中节点和地面节点之间的组网与互联,实现无缝隙的高效全球通信.另一方面,空间信息网处于高度开放的状态,缺少了物理隔离,这在方便信息传播的同时,也容易导致信息的泄露.因此,空间信息网络面临着巨大的安全挑战.隐蔽通信是一种重要的安全传输技术,当发送端向接收端发送信息时,能够保证非法窃听者检测到该传输的概率足够小,从而隐藏发送端的传输行为.利用隐蔽通信技术可以保障空间信息网络传输的可靠性与安全性.本文对空间信息网络的隐蔽通信进行综述,从背景介绍、关键技术、应用场景和未来挑战等几个方面介绍空间信息网络中隐蔽通信的研究工作与最新进展.

多维域低零功率通信

无线信道的开放性使得无线通信链路极易受到窃听和攻击.随着硬件设备的发展和信号处理技术的进步,无线通信链路面临的安全威胁日益严峻,亟需一种更为有效的防护机制保障无线通信链路的安全.为此,本文从能量博弈的角度提出了基于信号能量弥散的多维域低零功率通信体制,通过隐藏通信信号和行为来避免恶意用户对无线通信链路监听和攻击.该体制以直接序列扩频技术为基础,以通信行为的隐匿为目标,通过将信号能量在时、频、空、码和极化等多维参数空间进行弥散,增加侦听方的能量收集难度,提升信号的隐蔽性.本文以侦听方有关多维域信号参数的先验信息为基础定义信号的隐蔽性,并结合概率论、信息论和信号检测理论建立多维域低零功率通信系统的数学模型,分析了系统的可达性能极限,揭示了侦听方先验知识对隐蔽通信速率的影响,为后续研究工作的开展奠定了理论基础.结果显示通过信号能量的多维域弥散合法用户间的通信速率能够突破传统1/2次幂的变化规律,实现高效隐蔽的信号传输.

THE ANTHOCYANIN BIOSYNTHETIC REGULATOR MDMYB1 POSITIVELY REGULATES ASCORBIC ACID BIOSYNTHESIS IN APPLE

Ascorbic acid(AsA,vitamin C)is involved in the regulation of many aspects of plant growth and development.It is an essential micronutrient for humans and can prevent scurvy,maintain the health of gums and blood vessels,reduce the level of plasma cholesterol and enhance the immune systen.Apple cultivars Orin and Guanghui were crossed to obtain a group of hybrid offspring with and without red flesh in the course of assessing apple germplasm resources.Unexpectedly,the red-flesh apples had higher AsA contents than other apples.Further studies showed that the anthocyanin biosynthetic regulator MdMYBl directly activates the expression of dehydroascorbate reductase gene MdDHAR,thus promoting the activity of the DHAR enzyme and the accumulation of AsA.This finding reveals the mechanism leading to high AsA levels in red-flesh apples and suggests a new idea to cultivate red-flesh apples with high AsA contents and produce AsA efficiently and without pollution.